The present disclosure relates to a differential transformer type magnetic sensor using a planar coil and an image forming apparatus that detects a residual quantity of toner contained in a development part using the magnetic sensor.
In image forming apparatuses using toner as a developer, a magnetic sensor is used for detection of a residual quantity or a density of the toner. There are various types of magnetic sensors. A differential transformer type magnetic sensor has a configuration in which a drive coil, a differential coil functioning as a detection coil, and another differential coil functioning as a reference coil are disposed on the same core.
As the coils are formed into planar coils, the differential transformer type magnetic sensor can be made compact. As the differential transformer type magnetic sensor using the planar coils, a magnetic sensor in which a first coil (drive coil), a second coil (differential coil), a third coil (differential coil), and a fourth coil (drive coil) are disposed on a first layer, a second layer, a third layer, and a fourth layer respectively, and in which an insulating board is disposed between the neighboring layers is proposed.
Further, as the differential transformer type magnetic sensor using the planar coils, a magnetic sensor in which a first coil (drive coil) and a third coil (differential coil) are disposed in parallel on one surface of an insulating magnetic board, and in which a second coil (drive coil) and a fourth coil (differential coil) are disposed in parallel on the other surface of an insulating magnetic board is also proposed.